Many machines, such as large vehicles and ships, require a user to travel to various access points while the machine is both stationary and mobile. The access points may be internal to the machine, such as in a hull of a large ship. Alternatively, the access points may be external, such as in vehicles having elevated cabs and/or platforms that must be accessed by a user. The cab or platform access points may be elevated several feet above the ground surface, and therefore ladders, stairs, and handholds are often provided on the machine to allow the user to safely reach the desired access point. Additionally, the machine may include a railing around the perimeter of the elevated platform to prevent falls. While these safety measures help prevent falls, they require a certain level of dexterity and awareness by the user to be effective. Additionally, these measures typically have minimal utility once a user has lost his balance or is no longer in contact with the machine.
Other safety measures have been proposed that attempt to provide an additional level of safety to the user by independently supporting the user in the event of a fall. For example, British Application Publication No. BF 2,406,313 discloses a vehicle safety frame secured to a trailer bed of a truck. The frame includes a horizontally extending rail. A carriage runs inside the rail and carries a fall arrest block having retractable webbing. A harness worn by the user can be attached to the webbing. As the user moves vertically toward the rail, slack in the webbing is taken up by the fall arrest block. A break mechanism in the fall arrest block prevents the webbing from rapidly extending out of the block, such as during a fall. The user must climb a ladder without any attached safety feature, however, to initially retrieve the webbing for attachment to the harness. Additionally, the carriage is free to roll along the rail during use, thereby subjecting the user to unintended and uncontrolled lateral movement while supported by the webbing after a fall.
The previously proposed safety measures noted above do not adequately address fall safety in elevated cabs and platforms that require a user to routinely traverse a change in vertical elevation to reach desired access points on the machine. These limitations are exacerbated in large machines, such as track-type tractors, large wheel loaders, hydraulic excavators, and mining vehicles, where the change in vertical elevation is pronounced.